Change of State

Anytime there is a change in state, energy is involved. So far we have discussed the different phases of matter and the characteristics or properties of each phase of matter, now lets talk about how each phase of matter changes or becomes a new state or phase of matter. The first thing you need to have a change in state or phase is energy. Anytime there is a change in state, energy is involved.

Energy and Changes of State When state changes occur, matter goes from one physical form to another. To change states, energy must be added or removed from matter.

Melting: Solid to Liquid Melting is the change of state that occurs when energy is added to a solid and it becomes a liquid. The added energy causes the particles to lose their attraction for each other. As energy is added to a solid the particles begin to move quickly. Consequently the temperature rises. The temperature at which solid becomes liquid occurs is the melting point The first change we are going to look at is solid matter changing into liquid matter. The process of going from a solid to a liquid is called melting. Melting by definition is the change of state that occurs when energy is added (endothermic) to a solid and it becomes a liquid. The added energy causes the particles to lose their attraction towards each other. As energy is added to a solid the particles begin move more quickly, consequently the temperature rises. The temperature at which the solid actually becomes a liquid occurs is the melting point.

Freezing: Liquid to Solid Freezing the change in state that occurs when a liquid becomes a solid. The temperature at which a liquid becomes a solid occurs is the freezing point. Freezing is the opposite of melting, so freezing and melting occur at the same temperature. If energy is added, melting occurs, if energy is removed, freezing occurs. Freezing is an exothermic change because energy is removed from the matter causing the particles to lock into place. Next, lets look at what happens if matter is going from a liquid to a solid. Freezing is the change in state that occurs when a liquid becomes a solid. The temperature at which a liquid become a solid occurs is the freezing point. The freezing point of water is 0 degrees Celsius or 32 degrees Fahrenheit. Freezing is the opposite of melting, so freezing and melting occur at the exact same temperature…we will revisit this in a moment. If energy is added (endothermic) melting occurs, if energy is removed (exothermic) freezing occurs. Freezing is an exothermic change because energy is removed from the matter causing the particles to lock into place.

Vaporization: Liquid to Gas Vaporization is the change of state where a substance goes from a liquid state to a gas state. Evaporation is vaporization that occurs at the surface of a substance. (can occur below the boiling pt) Boiling is vaporization that occurs within/throughout the substance. Evaporation and boiling are endothermic changes. The temperature at which a liquid boils is the boiling point. There is a relationship between pressure and boiling point. As pressure decreases so does the boiling point. (direct relationship) Now we are going to look at the change in state from a liquid to a gas. Vaporization is the change of state where a substance goes from a liquid to a gas. Vaporization describes the entire process of changing state, but there are two levels of this change of state. Evaporation is vaporization that occurs at the surface of a substance, this can occur below the actual boiling point, and boiling is vaporization that occurs within or throughout the substance. Both boiling and evaporation together causes vaporization. Evaporation and boiling are both endothermic changes which means energy is being added and therefore vaporization as a whole is an endothermic change. The temperature at which a liquid boils is the boiling point. There is a relationship between pressure and boiling point. As pressure decreases do does the boiling point. This is considered a direct relationship. Vaporization occurs at the Vaporizatioat 100 degrees Celsius or 212 degrees Fahrenheit.